Kunzite (called Malachite in the English anime) is the fourth and final member of the Shitennou. He carries a shortsword, and Takeuchi describes him as the greatest of the four, with the majesty of an Arabian king. She also admits to being very fond of him as a character. He is about 25-26 years old, leads the Dark Kingdom's Middle Eastern Division, and is named after the mineral kunzite (or, in the dub, malachite).

In the manga, Kunzite is first shown acting in an advisory role to Zoisite, often helping the younger, less experienced king formulate plans of attack for gathering energy. Kunzite showed little regard for the fate of his fellow Shitennou and indeed seemed rather impassive when Jadeite, Nephrite, and Zoisite were killed off. Even so, Queen Beryl tells Kunzite that if they recover the Ginzuishou the fallen Shitennou could then be revived. As per Queen Beryl's orders, Kunzite attacked the Sailor Senshi at the Tokyo Tower and defeated them swiftly. Sailor Moon was about to be destroyed by Kunzite's attack when Tuxedo Mask jumped in and took the hit for her, nearly killing himself in the process. Her heart broken by his sacrifice, she regained her memories as the Moon Princess and the Ginzuishou appeared, the light washing over everyone including Kunzite. In this moment he too regained his memories of the past and was torn between his loyalty to Beryl and Endymion. He witnessed the brief rebirth of his fellow Shitennou but they quickly decomposed into their mineral forms again. Beryl then ordered Kunzite to capture the Princess and her Silver Crystal. Confused by his emotions and newfound memories Kunzite instead takes Mamoru with him back to the Dark Kingdom. Upon questioning Beryl about the Shitennou and Endymion, she tells him that they cannot be revived now that their bodies have turned to stone. Also, upon hearing Kunzite call Mamoru by his true name, Endymion, she ramps up her brainwashing and implants a shard of kunzite crystal into his forehead. This leaves Kunzite little more than a zombie. In a blind rage Kunzite again attacks the Senshi, singling out Sailor Moon and attempting to wrestle the Ginzuishou away from her. They fly up into the atmosphere where they battle ferociously but in the end Kunzite is defeated by a Sailor Planet Attack, leaving only the piece of kunzite stone behind. In the final battle against Queen Metaria it was Kunzite who traversed the dimensions and appeared to Mamoru to inform him that the creature's weakness lay in a point on its forehead, which he and Usagi managed to exploit and end the demon queen's plans of conquest for good.

In the anime, Kunzite was first shown with Zoisite plotting against the second king, Nephrite. The two were quite obviously lovers and Zoisite would cling to Kunzite for support and guidance. Together they managed to collect all seven of the Rainbow Crystals but just when things were looking up for the Dark Kingdom, Zoisite made a grave mistake and attacked Tuxedo Mask with an ice crystal. This cost him his life and revealed Sailor Moon as the Moon Princess, also awakening the power of the Ginzuishou. Zoisite was killed for his disobedience and Kunzite fell into a depression, though his loyalty to Queen Beryl did not waver in the slightest. He took the injured Mamoru back to the Dark Kingdom as per Beryl's instructions and he was transformed into an agent of the Dark Kingdom. Kunzite greatly resented being forced to work with Endymion but nevertheless carried out his assignments out of obedience. He grew increasingly suspicious of Endymion because he would foil Kunzite's plans and continue to, in a somewhat macabre way, protect Sailor Moon and the senshi, believing that innocent humans need not be harmed in the process of achieving their goals. Beryl herself began to doubt Endymion's loyalty and gave Kunzite the task of keeping tabs on Endymion. After many defeats Endymion was cured of Beryl's brainwashing, albeit temporarily, then whisked away to the Dark Kingdom again. The Senshi resolved to find the entrance to the Dark Kingdom, recover Mamoru, and end the threat once and for all. Kunzite met them in battle at the D Point during which the Senshi's past memories of the Moon Kingdom were restored. Kunzite lashed out with an energy boomerang attack that took out all the senshi except for Sailor Moon. In a last defiant effort Kunzite attacked her but the projectile was deflected back at him and pierced him. He died crying out to Zoisite, begging his love to meet him on the other side.

Are aliens really out there? When it comes to Bishoujo Senshi Sailor Moon Crystal, they’re not only here, they’re everywhere! It’s not just the evil aliens that we see the sailor squad fighting either; the girls themselves are also aliens, each from a different planet in the solar system.